DNP-enhanced ultrawideline 207Pb solid-state NMR spectroscopy: an application to cultural heritage science

Abstract

Dynamic nuclear polarization (DNP) is used to enhance the (ultra)wideline ²⁰⁷Pb solid-state NMR spectra of lead compounds of relevance in the preservation of cultural heritage objects. The DNP SSNMR experiments enabled, for the first time, the detection of the basic lead carbonate phase of the lead white pigment by ²⁰⁷Pb SSNMR spectroscopy. Variable-temperature experiments revealed that the short T′₂ relaxation time of the basic lead carbonate phase hinders the acquisition of the NMR signal at room temperature. We additionally observe that the DNP enhancement is twice as large for lead palmitate (a lead soap, which is a degradation product implicated in the visible deterioration of lead-based oil paintings), than it is for the basic lead carbonate. This enhancement has allowed us to detect the formation of a lead soap in an aged paint film by ²⁰⁷Pb SSNMR spectroscopy; which may aid in the detection of deterioration products in smaller samples removed from works of art.